Most winemakers worry that mold will ruin their grape harvest. But it turns out that for some, the blight is all right.

Botrytis, or “noble rot,” is a fast-growing mold that sets in after early fall rains. In moderate quantities, it’s actually beneficial to help grapes attain a better flavor and more sweetness, especially for chardonnay grapes. Grapes with even thicken skins, like cabernet sauvignon, seems to resist rot. But a lot of rot can turn a harvest into a questionable commodity while winemakers wait for sugar levels to rise to their optimum brix.

“Once it starts, it rots by the hour,” said John Balletto of Baletto Vineyards in Santa Rosa, about one hour north of San Francisco and about 30 minutes west of Napa and Sonoma Counties. “It was so stressful. At one point, we had 1,200 tons of chardonnay that was not harvested.”

How it works: The botrytis evaporates water content and concentrates the sugar levels, acid and flavors in the grapes. One wine in particular, Dolce Vineyards, a producer of a rare dessert wine in Napa, embraces the rot’s honeysuckle characteristics. “For us, it’s a good thing,” said Dirk Hampson, Dolce’s creator and director of winemaking. It’s a partner to the heralded Far Niente Winery in Napa.